Installation for microwave heating of a product held in containers

ABSTRACT

The installation includes a microwave heater station ( 14 ) having a microwave applicator, and a support ( 10 ) suitable for supporting the receptacles ( 12 ) in the heater station. The support ( 10 ) has at least one receptacle zone ( 20 ) which is defined by the surface ( 10 A) of the support and by a metal band ( 24 A,  24 B) fixed to the support. The zone ( 20 ) serves to support a receptacle ( 12 ) whose bottom stands on the surface ( 10 A) of the support and whose side wall ( 12 B) is surrounded by the band. The support can be a conveyor bringing the receptacles into the heater station.

BACKGROUND OF THE INVENTION

The invention relates to an installation for heating a substancecontained in receptacles by applying microwaves thereto, theinstallation comprising a microwave heater station having microwaveapplication means, and a support suitable for supporting the receptaclesin the heater station.

It is known from Patent Application PCT/FR01/02698 that, in order toensure that a substance contained in receptacles is heated uniformly, itis advantageous to provide an end wall (the bottom or the lid) of eachof the receptacles with an uninterrupted extra thickness of dielectricmaterial, and to limit the extent to which microwaves pass through theside wall of each of the receptacles by providing said side wall with anelectrically conductive material that reflects microwaves.

Heating by applying microwaves concerns domestic applications, forheating up or for defrosting (thawing) food. It also concerns industrialapplications, in which microwaves are used for pasteurizing orsterilizing a substance, in particular food, contained in a receptacle.

The above-mentioned patent application proposes for the receptacle to beformed by a tray directly containing the substance to be heated by themicrowaves. The receptacle can also be a utensil in which a traycontaining such a substance can be disposed for heating said substancein a microwave oven, e.g. a domestic microwave oven. That patentapplication also proposes disposing a utensil of that type on theconveyor of a microwave heating installation, the utensil serving toreceive trays containing a substance to be heated by applying microwavesthereto in that installation, in particular for pasteurizing andsterilizing the substance.

Such a known installation operates quite satisfactorily, but at a costthat is relatively high. A large number of utensils must be disposed onthe conveyor in order for the installation to operate at an industrialrate of throughput.

Unfortunately, the cost of each utensil is relatively high. The extrathicknesses are disposed on the bottoms of the utensils, and the traysof substance that are to be disposed in those utensils must have theirbottoms provided with cavities suitable for receiving said extrathicknesses.

The installation serves to pasteurize or sterilize the substancecontained in the trays, but, prior to being consumed, said substancemust generally be heated up again by the consumer in a domesticmicrowave oven. Since the trays must be shaped as indicated above inorder to fit the specific shape of the utensils on the conveyor, it isdifficult to provide the trays with means enabling the distribution ofthe microwaves to be made uniform during said heating in a domesticmicrowave oven.

Thus, with an installation of the type known from the prior art, thesubstance contained in the trays can be satisfactorily sterilized andpasteurized, but that generates a relatively large extra cost for theinstallation, and prevents the trays from offering the possibility ofbeing heated uniformly in preparation for consumption of the substance,so that the consumer always finds zones that are cold or zones that aretoo hot in the substance contained in the trays.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to remedy those drawbacks, or atleast to mitigate them.

In an installation of the invention, the heater station may be thecavity of a microwave oven, the support then being the bottom of thecavity or a shelf placed therein.

For example, the installation may be applied to an automatic dispenserof pre-cooked dishes that are heated in said dispenser.

The dispenser may have a dish storage portion (optionally refrigerated),means for transferring the dishes from the storage portion to the heaterstation, and means for removing the dishes, the various means beingactuated in response to the consumer making an order (payment) and aselection.

An object of the invention is to provide an installation that makes itpossible, inexpensively, to heat uniformly the substance contained inthe receptacles, without requiring costly utensils to be formed and putin place in the heater station.

This object is achieved by the fact that the support has at least onereceptacle zone which is defined by the surface of said support and by ametal band held on the support, said zone serving to support areceptacle whose bottom is placed on the surface of the support andwhose side wall is surrounded by the band.

By means of these provisions, the support has a configuration that isextremely simple because a simple metal band is fixed to the support.The inside shape of said band can easily be designed such that itmatches conventional trays. In particular, it is not necessary for thebottom of each of the trays to be provided with a cavity. The metal bandis, in itself, an element that is inexpensive, that is optionally madeof a single material, and that is easy to fix to the support. The bandlimits, or even prevents, the penetration of microwaves into thereceptacles, via the side walls of said receptacles. However, themicrowaves can penetrate freely into the receptacles via their top andbottom faces.

Advantageously, the support is a conveyor which is suitable for bringingthe receptacles into the heater station, and the conveyor has receptaclezones, each of which is defined by the surface of the conveyor and by ametal band fixed to the conveyor, each zone serving to support areceptacle whose bottom is placed on the surface of the conveyor andwhose side wall is surrounded by the band.

Advantageously, the conveyor is made up of at least two elements whichremain substantially stationary relative to each other, over the paththat they travel between the inlet and the outlet of the heater station,and which move relative to one another outside said path, and at leastone band is a hinged band which comprises two band portions secured torespective ones of each of said elements.

For example, the conveyor is a conveyor belt made up of a plurality ofslats, and each band is made up of two portions, each of which issecured to a respective one of two different slats of the conveyor.

For example, the two elements of the conveyor that are mounted to moverelative to each other (the slats of the conveyor belt) are made of aplastics material such as polypropylene. Each of the various portions ofthe band in question is fixed to a respective one of the elements of theconveyor. Thus, the elements can move relative to each other withouthindrance, but the portions of the band are disposed such that, when theelements of the conveyor take up the relative position that they occupyin the heater station, the portions of the band, as considered together,form a metal band suitable for surrounding the side wall of a receptacledisposed in the receptacle zone defined by the band.

The invention also relates to an assembly made up of an installation ofthe invention, and of receptacles serving to contain the substance thatis to be heated by microwaves in said installation.

According to the invention, each of the receptacles has an end wall,namely a bottom or a lid, which has extra thickness formed of adielectric material.

With the invention, it is the receptacles that can have the extrathickness of dielectric material, while the bands made ofmicrowave-reflecting material are disposed on the support. Thus, when areceptacle containing the substance to be heated (pasteurized, orsterilized) by microwaving is disposed in the receptacle zone defined bya band, heating is distributed uniformly throughout the substancecontained in the receptacle because the microwaves are concentrated atthe bottom of the receptacle by the dielectric extra thickness withwhich said bottom is provided, while said microwaves are prevented fromacting against the side wall of the receptacle by the metal band.

Then, when the consumer of the substance contained in the receptaclewishes to heat the substance in order to consume it, said consumerplaces the receptacle (a tray) in a domestic microwave oven. During thisheating stage, the extra thickness acts to concentrate the microwaves,and cold zones are avoided or at least limited in the central region ofthe receptacle, although to a lesser extent than with trays having bothextra thickness and surrounding metal, as in Patent ApplicationPCT/FR01/02968.

It should be noted that the power of the microwaves in a domestic ovencan be lower than their power in pasteurization or sterilizationinstallations. Thus, the overall heating time for which the substance isheated can be increased slightly when said substance is contained in areceptacle having extra thickness of a dielectric material, but themicrowaves are distributed much more uniformly than with a receptacledevoid of such extra thickness, and the consumer enjoys the satisfactionof consuming a substance that is heated uniformly.

Preferably, each receptacle has a side wall which defines a peripheryanalogous to the inside shape of the metal band.

Advantageously, each receptacle comprises a side wall and a bottomformed integrally with each other and of the same material.

Frequently, receptacles containing a substance to be heated up bymicrowaves are disposable. It is desirable firstly for such receptaclesto be inexpensive, and secondly for them to be easy to recycle. Areceptacle whose side wall and whose bottom are formed of a singlematerial is thus considerably less costly than the receptacle describedby Patent Application PCT FR/01/02698, while also offering, whencombined with the metal band of the installation, the same quality ofsterilization or of pasteurization by microwaving.

The invention will be well understood and its advantages will appearmore clearly on reading the following detailed description of anembodiment shown by way of non-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall side view of an installation of the invention;

FIG. 2 is a section view seen looking along arrows II—II of FIG. 1; and

FIG. 3 is a fragmentary perspective view seen looking arrow III of FIG.1.

DETAILED DESCRIPTION OF THE INVENTION

The installation shown in FIG. 1 comprises a conveyor 10 on whichreceptacles 12 containing a substance to be treated with microwaves canbe disposed, and which can convey said receptacles through a microwaveheater station 14. Microwave application means of a type known per seare disposed in said station 14. It is recalled that microwaves areelectromagnetic waves whose frequency lies in the range 0.3 GHz to 300GHz, and more particularly in the range 0.3 GHz and 5.2 GHz.

Upstream from the station 14 in the advance direction F in which theconveyor advances, the installation includes a receptacle loadingstation 16 in which the receptacles 12 are put in place on the conveyor.For example, the loading station comprises receptacle support anddeposit means 18 suitable for carrying the receptacles and for disposingthem in the receptacle zones 20 of the conveyor.

In the example shown, the receptacles 12 which are put in place on theconveyor in the station 16 are already filled with substance to besubjected to microwaves, and are already closed. It is also possible toimagine the installation having means for continuously disposing emptyreceptacles on the conveyor, a metering and filling station for fillingeach of the receptacles with a metered quantity of substance that is tobe subjected to microwave treatment, and a station for closing saidreceptacles, e.g. by sealing a peel-off strip over the top opening ineach of said receptacles, the various stations being disposed upstreamfrom the station 14. The support (conveyor) is, at least in thereceptacle zones 20, devoid of elements, in particular metal elements,that prevent or limit propagation of microwaves.

Downstream from the station 14, the installation includes a station 22for removing the receptacles 12, which station takes hold of thereceptacles in the receptacle zones in order to carry them to means forpackaging them and for putting them onto pallets.

The installation can also include a warming station (not shown) in whichthe receptacles are maintained at a temperature for a time such that thetime/temperature pair complies with a desired pasteurization value.

The warming station is disposed downstream from the station 14,optionally following on from the station 22.

For example, the warming station operates with a heated fluid (air orwater).

As can be seen more clearly in FIG. 3, each of the receptacle zones 20is defined by the surface 10A of the conveyor and by a metal band fixedto the conveyor. In the advantageous example shown, each metal band ismade up of two half-band portions 24A and 24B. Said half-bands are fixedto the surface of the conveyor, and each zone 20 can thus support areceptacle whose bottom 12A is placed on the surface 11A of the conveyorand whose side wall 12B is surrounded by the band 24A, 24B.

The conveyor 10 is made up of a plurality of slats 11A, 11B which extendtransversely to the advance direction F in which the conveyor advances,and which are fixed together in mutually hinged manner. It can be seenthat, over the entire top path of the conveyor, lying between thestations 16 and 22, the various slats 11A, 11B remain stationaryrelative to each other. Conversely, at the ends of the conveyor, saidconveyor is supported by transverse rollers 8 that enable it to go roundin a loop. In the regions of the rollers 8, the conveyor must take up asmall radius of curvature determined by the radius of curvature of therollers, and the various slats that make up said conveyor angularlyposition themselves relative to one another accordingly.

For each band, the first half-band 24A is secured to one slat 11A of theconveyor, and the second half-band 24B is secured to another slat 11Badjacent to the first slat. Thus, as seen in FIG. 1, the band tends toopen in the end regions of the conveyor because the two half-bands moveapart from each other, correspondingly to the relative displacement ofthe slats 11A and 11B.

Outside the small radius of curvature zones, and in particular in thestation 14, each of the bands forms an almost continuous band.

However, it can be observed in FIGS. 1 and 3 that, even over the pathtraveled by the elements of the conveyor between the stations 16 and 22and, more precisely, between the inlet and the outlet of the heaterstation 14, the two half-bands 24A and 24B are disposed such that a gapj exists between them. This gap is narrow, and, for example, it lies inthe range 0.5 millimeters (mm) to 3 mm, it preferably being about 1 mm.

A gap that is too wide would prevent the band locally from acting as amicrowave reflector element, and could lead to considerable localheating in a region of the receptacle that is close to the gap betweenthe two half-bands. However, since the two half-bands are mounted tomove relative to each other, it would be difficult, unless they aremanufactured with extremely great precision and thus at high cost, toguarantee full contact between their facing edges when they are in their“treatment” position, which is the position that they occupy inparticular in the station 14. If the contact between the two half-bandsis incomplete, there is a risk of electric arcs striking between thefacing edges of the two half-bands that are in partial contact. Choosinga narrow gap j between the facing edges makes it possible to avoid thatrisk.

It can be seen in the figures that the bands are spaced apart from oneanother. This spacing makes it possible to prevent electric arcs fromstriking in the station 14 between two bands. Preferably, the spacing Ain the direction F and the spacing B transversely to that direction areboth at least 0.5 centimeters (cm) so as to avoid risks of interferencebetween the waves reflected by the various bands in the heater station14.

It could be imagined for the wall of each band to form a continuouswhole, which would also prevent electric arcs from striking. Inparticular such a continuous band could be disposed on a conveyor notmade up of elements that are mounted to move relative to one another.For example, such a conveyor could be a carousel conveyor.

However, certain carousel conveyors are also made up of elements thatmove relative to one another, and it should be understood that the bandsmade up of a plurality of portions as shown in FIGS. 1 to 3 can also beused on such conveyors.

The band portions 24A and 24B are fixed to the conveyor by fixing tabs,respectively 25A and 25B. For example they are metal tabs, formedintegrally with the respective half-bands. They can be fixed by anysuitable means to the surface of the conveyor, e.g. by adhesive bonding,or else by riveting. In which case, it is preferable for the rivets 26to be made of a plastics (dielectric) material, thereby preventingelectric arcs from striking in the regions in which the bands are fixedto the conveyor.

FIG. 2 shows the configuration of three bands in which receptacles aredisposed at the inlet 14A of the station 14, which inlet is formed by aslot that extends transversely to the direction F.

Naturally, over the “go” path of the conveyor, between the stations 16and 22, the outside face 10A of the conveyor on which the bands arefixed faces upwards. FIGS. 2 and 3 also show the “return” path of theconveyor on which the bands face downwards.

In order to support the conveyor over the return path, the installationincludes at least one elongate support element 28. Said elongate supportelement extends parallel to the advance direction F in which theconveyor belt formed by the conveyor advances, is disposed under saidconveyor belt, and penetrates into a space 29 provided between adjacentrows of bands so as to co-operate with the outside face 10A of theconveyor belt over the return path of said conveyor belt. In thisexample, two elongate support elements 28 are disposed under theconveyor and go between the fixing tabs on adjacent receptacles in thesame row so as to co-operate with the face 10A of the conveyor.

Each of the receptacles 12 which are disposed in the receptacle zones ofthe installation has a bottom wall 12A which has extra thickness 13A ofdielectric material. For example, the height of the extra thickness liesin the range 2 mm to 6 mm, the ratio between the height and the depth ofthe receptacle advantageously being less than 0.3, and preferably about0.1.

For each receptacle, the extra thickness covers a portion of the bottomof the receptacle and its area is, for example, about 1/10^(th) to ½,and preferably about ⅓ of the area of the bottom of the receptacle.

The extra thickness is disposed in a central region of the receptacleand it is made of a dielectric material which does not reflect themicrowaves, and whose dielectric constant lies in the range 1.5 to 3,and preferably greater than 2.

For example, the extra thickness may be formed in a dielectric materialsuch as Teflon, mica, Samicanite, propylene, or glass. For example, thereceptacle can be made of polypropylene or of glass, in which case theextra thickness is advantageously formed integrally with saidreceptacle. Advantageously, the bands 24A, 24B have a height h at leastsubstantially equal to 80% of the height H of the side walls of thereceptacles. This corresponds substantially to the level of filling ofthe substance inside the receptacles, and the band thus forms a“protective” band off which microwaves are reflected in order to preventthe substance contained in the receptacle from “overheating”, and whichis disposed against the side walls of said receptacle.

Naturally, it is advantageous for the periphery of the side wall 12B ofeach of the receptacles to be analogous to the inside shape of a band.

1. An assembly comprising: an installation for heating a substance byapplying microwaves thereto, removable receptacles for containing thesubstance to be heated by microwaves in said installation, wherein eachof the receptacles has a bottom formed integrally with the receptacleand having extra thickness formed of a dielectric material, and a sidewall, wherein the side wall is transparent to microwaves; theinstallation having a microwave heater station including microwaveapplication means, and a support suitable for supporting the receptaclesin the heater station, the support having at least one receptacle zonedefined by the surface of said support and by a metal band secured tothe support, said zone serving to support the receptacle bottom or lidplaced on the surface of the support, and the band surrounding the sidewall.
 2. An assembly according to claim 1, wherein each receptacle sidewall defines a periphery analogous to an inside shape of a band.
 3. Anassembly according to claim 1, wherein each receptacle side wall andbottom are formed integrally with each other and of the same material.4. An assembly according to claim 1, wherein the band has a height atleast substantially equal to 80% of the height of the side walls of thereceptacles.
 5. An assembly according to claim 1, wherein said extrathickness is formed in a central region of said end wall.
 6. An assemblycomprising: an installation for heating a substance contained inreceptacles by applying microwaves thereto; removable receptacles forcontaining the substance to be heated by microwaves in saidinstallation, wherein each of the receptacles has a bottom formedintegrally with the receptacle and having extra thickness formed of adielectric material, and a side wall transparent to microwaves; theinstallation comprising a microwave heater station having microwaveapplication means, and a conveyor for bringing the receptacles into theheater station and for supporting the receptacles in said station, theconveyor having receptacle zones, each of which is defined by a surfaceof the conveyor and by a metal band secured on the conveyor, each zoneserving to support one of the receptacle bottoms or lids placed on thesurface of the conveyor and the band surrounding the side wall.
 7. Anassembly according to claim 6, wherein said extra thickness is formed ina central region of said end wall.
 8. An installation for heating asubstance contained in receptacles by applying microwaves thereto, theinstallation comprising a microwave heater station having microwaveapplication means, and a conveyor suitable for bringing the receptaclesinto the heater station and for supporting the receptacles in saidstation, the conveyor having receptacle zones, each of which is definedby a surface of the conveyor and by a metal band fixed to the conveyor,each zone serving to support a receptacle having a bottom placed on thesurface of the conveyor and a side wall surrounded by the band; whereinthe conveyor includes at least two elements which remain substantiallystationary relative to each other, over a path that said elements travelbetween the inlet and the outlet of the heater station, and which moverelative to one another outside said path, at least one band being ahinged band including two band portions secured to respective ones ofeach of said elements.
 9. An installation according to claim 8, whereinthe two portions of the hinged band are disposed to define a gap betweenthem over the path traveled by the elements of the conveyor whichcarries them between the inlet and the outlet of the heater station. 10.An installation according to claim 9, wherein the gap lies in the range0.5 mm to 3 mm.
 11. An installation according to claim 10, wherein thegap is substantially equal to 1 mm.
 12. An installation according toclaim 8, wherein the conveyor is a conveyor belt comprising a pluralityof slats, and each band comprises two portions, each of which is securedto a respective one of two different slats of the conveyor.
 13. Aninstallation according to claim 12, wherein the conveyor belt is drivenalong a go path over which the bands face upwards, and along a returnpath over which the bands face downwards, the installation including atleast one elongate support element which extends parallel to an advancedirection in which the conveyor belt advances, which is disposed underthe conveyor belt, and which penetrates into a space provided betweenadjacent rows of bands in order to co-operate with the outside face ofthe conveyor belt over the return path of said conveyor belt.
 14. Aninstallation according to claim 8, wherein the bands are spaced apartfrom one another.
 15. An installation according to claim 8, havingseveral bands of which the walls form a continuous whole.
 16. Anassembly comprising the installation according to claim 15, andreceptacles serving to contain the substance that is to be heated bymicrowaves in said installation, wherein each of the receptacles has anend wall comprising a bottom or a lid, which has extra thickness formedof a dielectric material.
 17. An assembly according to claim 16, whereineach receptacle has a side wall defining a periphery analogous to aninside shape of a band.
 18. An assembly according to claim 16, whereineach receptacle comprises a side wall and a bottom formed integrallywith each other and of the same material.
 19. An assembly according toclaim 16, wherein the band has a height at least substantially equal to80% of the height of the side walls of the receptacles.
 20. A processfor heating a substance, comprising: providing an installation having amicrowave heater station including microwave application means, and asupport suitable for supporting receptacles in the heater station, thesupport having at least one receptacle zone defined by the surface ofsaid support and by a metal band secured on the support configured forsupporting a receptacle, said zone serving to support a receptaclebottom placed on the surface of the support; providing a removablereceptacle containing the substance to be heated by microwaves in saidinstallation, wherein the receptacle has a bottom formed integrally withthe receptacle having extra thickness in a central portion formed of adielectric material, and a side wall transparent to microwaves; placingthe receptacle containing the substance in the receptacle zone of themicrowave heater station; and applying microwaves to the substance inthe receptacle.
 21. An assembly comprising: an installation for heatinga substance by applying microwaves thereto, removable receptacles forcontaining the substance to be heated by microwaves in saidinstallation, wherein each of the receptacles is removable and includesmeans for concentrating the microwaves and formed integrally with abottom of the receptacle, and wherein the bottom comprises an extrathickness formed of a dielectric material, and a side wall transparentto microwaves; the installation having a microwave heater stationincluding microwave application means, and a support suitable forsupporting the receptacles in the heater station, the support having atleast one receptacle zone defined by the surface of said support and bymeans for reflecting microwaves secured to the support, wherein saidmeans for reflecting microwaves comprise a metal band, said zone servingto support the receptacle bottom or lid placed on the surface of thesupport, and the band surrounding the side wall.
 22. An assemblyaccording to claim 21, wherein each receptacle has a side wall defininga periphery analogous to an inside shape of a band.
 23. Art assemblyaccording to claim 21, wherein each receptacle comprises a side wall anda bottom formed integrally with each other and of the same material. 24.An assembly according to claim 21, wherein the band has a height atleast substantially equal to 80% of the height of the side walls of thereceptacles.